LPS3015 Просмотр технического описания (PDF) - Microchip Technology

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LPS3015

High Voltage Input Integrated Switch Step-Down Regulator

Microchip Technology 

5.0 APPLICATION INFORMATION

5.1 Typical Applications

The MCP16301 step-down converter operates over a

wide input voltage range, up to 30V maximum. Typical

applications include generating a bias or VDD voltage

for the PIC® microcontrollers product line, digital con-

trol system bias supply for AC-DC converters, 24V

industrial input and similar applications.

5.2 Adjustable Output Voltage

Calculations

To calculate the resistor divider values for the

MCP16301, Equation 5-1 can be used. RTOP is con-

nected to VOUT, RBOT is connected to GND and both

are connected to the VFB input pin.

EQUATION 5-1:

RTOP

=

RBOT

×

⎛

⎝

V----O----U---T-

VFB

–

1⎠⎞

EXAMPLE 5-1:

VOUT = 3.3V

VFB = 0.8V

RBOT = 10 kΩ

RTOP = 31.25 kΩ (Standard Value = 31.2 kΩ)

VOUT = 3.3V

EXAMPLE 5-2:

VOUT = 5.0V

VFB = 0.8V

RBOT = 10 kΩ

RTOP = 52.5 kΩ (Standard Value = 52.3 kΩ)

VOUT = 4.98V

The transconductance error amplifier gain is controlled

by its internal impedance. The external divider resistors

have no effect on system gain, so a wide range of

values can be used. A 10 kΩ resistor is recommended

as a good trade-off for quiescent current and noise

immunity.

MCP16301

5.3 General Design Equations

The step down converter duty cycle can be estimated

using Equation 5-2, while operating in Continuous

Inductor Current Mode. This equation also counts the

forward drop of the freewheeling diode and internal

N-Channel MOSFET switch voltage drop. As the load

current increases, the switch voltage drop and diode

voltage drop increase, requiring a larger PWM duty

cycle to maintain the output voltage regulation. Switch

voltage drop is estimated by multiplying the switch

current times the switch resistance or RDSON.

EQUATION 5-2: CONTINUOUS INDUCTOR

CURRENT DUTY CYCLE

D = (---V----I-(-N-V---–-O---U-(--I-T-S---W+-----×-V----DR---i-D-o--dS---eO--)-N----)--)-

The MCP16301 device features an integrated slope

compensation to prevent the bimodal operation of the

PWM duty cycle. Internally, half of the inductor current

down slope is summed with the internal current sense

signal. For the proper amount of slope compensation,

it is recommended to keep the inductor down-slope

current constant by varying the inductance with VOUT,

where K = 0.22V/µH.

EQUATION 5-3:

K = VOUT ⁄ L

For VOUT = 3.3V, an inductance of 15 µH is

recommended.

TABLE 5-1:

VOUT

2.0V

3.3V

5.0V

12V

15V

RECOMMENDED INDUCTOR

VALUES

K

0.20

0.22

0.23

0.21

0.22

LSTANDARD

10 µH

15 µH

22 µH

56 µH

68 µH

© 2011 Microchip Technology Inc.

DS25004A-page 17

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